As a technology of signal control, pulse density modulation (PDM) is widely applied in electronic circuits, such as communication devices, power control devices, and tuning units. Particularly, PDM can be used in an automatic gain controller (AGC) and/or an automatic frequency controller (AFC) in mobile terminals for transmission power control and tuning control respectively.
For example, when using PDM for automatic gain control, in order to control a transmission power to a target power value, a corresponding PDM value needs to be set. In practice, only the PDM values of several points calibrated in advance are generally stored. As the target power value is not necessarily on these points, a corresponding PDM value needs to be calculated through linear interpolation.
However, the relationship between the PDM value of an actual chip and the corresponding power value is not an ideal linear one. That is, an integral non-linear (INL) error exists. Therefore, when automatic gain control is conducted using a PDM value calculated through linear interpolation, an error of the actual power value is caused by the INL error, thus leading to a relatively long ping-pong time, that is, it requires a plurality of adjustments for the PDM value to finally reach the target power value.
For automatic frequency control, a similar problem also exists that an error of an actual frequency value is caused when using PDM tuning and that it requires a plurality of adjustments for PDM before reaching a target frequency value. The above-mentioned problems caused by INL errors are not limited to AGC and AFC, but will affect any circuits using a PDM value.